Syringes which can prevent or reduce the probably of contaminated infection are in high demand, and those syringes which can offer a utility of operation which approaches or exceeds that of a non-safety syringe are in even higher demand. Some of the safety syringes which are known include U.S. Pat. No. 4,710,170, issued on Dec. 1, 1987 and entitled "Anti-Needle Strike and Anti-Drug Abuse Syringe" enabled the cannula to be withdrawn into the cylinder, and compressibly destroyed with the stem. U.S. Pat. Nos. 4,770,655 and 4,804,370, issued on Sep. 13, 1988 and Feb. 14, 1989 respectively and both entitled "Disease Control Syringe Having a Retractable Needle" enabled the cannula to be withdrawn into the cylinder, automatically canted to one side, and compressibly destroyed. All of the above mentioned syringes were invented by Terry M. Haber, William H. Smedley, and Clark B. Foster, the inventors of the present application.
One of the later designs includes U.S. Pat. No. 4,931,040, issued on Jun. 5, 1990 and entitled "Safety Syringe Having a Combination Needle Cannula and Articulating Hub for Retracting said Cannula into a Medication Carpule," and also issued to the inventors of the present application. In that invention a separate safety syringe was designed to accept a disposable, pre-filled capsule which was commercially known under the name CARPULE. The safety syringe could be used with any number of pre-filled capsules.
The disadvantages of that design includes a factor relating to the separability of the safety syringe from the capsules. One might be present, with the need to search for the other. Further, any re-usable structure raises concerns relating to sterility and cleanliness. When used in the surgical theater, a single drop from tainted blood could become lodged on a surface of the safety syringe to be later ejected onto another patient. Sterilization was also an issue. Where plastic was chosen for the safety syringe, continual re-sterilization could cause breakdown of materials or weakening of the material structure.
In the structures disclosed in the U.S. Pat. No. 4,931,040 the user would be required to load in a fresh capsule, use the syringe, retract the cannula and remove the capsule and load in a new capsule. The time required was slight, but in emergency room use, seconds are valuable. When action is required, the limitation of waiting until an old capsule can be removed and a new one loaded can be severe.
What is needed is a completely disposable syringe which is available in a pre-loaded condition and which can be used immediately by medical personnel. The cannula should be withdrawable at the leisure of the user, and the withdrawing action should be as brief as possible. The withdrawal procedure should render the syringe totally unusable, and safe disposal should be facilitated.